Two days before the 15 year anniversary of the September 11 attack, moments ago the House unanimously passed - to thunderous applause - legislation allowing the families of 9/11 victims to sue Saudi Arabia in U.S. courts, The bill, which passed the Senate unanimously in May, now heads to President Obama’s desk. And that's where things get tricky for Obama.

The White House has fiercely opposed the bill, arguing it could both strain relations with Saudi Arabia and also lead to retaliatory legislation overseas against U.S. citizens. Obama has lobbied fiercely against the bill, and has hinted strongly it will veto the measure.

He is not alone: the Saudi government has likewise led a vocal campaign in Washington to kill the legislation. Those efforts have been fruitless in Congress, however. Meanwhile, the legislation saw broad support from both parties, and Congress could override an Obama veto for the first time if he rejects the legislation. Such an outcome would undoubtedly embarrass Obama and divide Democrats ahead of the 2016 elections and a crucial lame-duck session of Congress.

For now, Obama is adamanat: "The Saudis will see this as a hostile act," said Dennis Ross, Obama’s former Middle East policy coordinator. "You’re bound to see the Obama administration do everything they can to sustain a veto."

How Obama will spin such a pro-Saudi, and anti-US decision, which may be overriden anyway, to the US population is unclear.

To an extent, Obama finds himself between a rock and a hard place. As we reported in April, Saudi officials threatened the enactment of the law could lead them to sell off the kingdom’s U.S. Treasury debt and other American assets, which the officials told lawmakers and U.S. officials totaled $750 billion, according to the New York Times. The Saudi government held $117 billion in U.S. Treasury debt in March, according to Treasury figures obtained by Bloomberg. The kingdom may have additional holdings not included in the data on deposit with the New York Federal Reserve Bank, in entities in third countries, or through positions in derivatives.

According to the Hill, lawmakers on Capitol Hill are unsure whether Obama will actually use his veto pen on the Justice Against Sponsors of Terrorism Act. “I presume they would have to think very carefully about a veto because it might very well be overridden,” said Nadler.

To override the president, supporters would need a two-thirds majority in each chamber. “I think the votes will be there to override it,” said Rep. Pete King (R-N.Y.), who introduced the bill in the House.

As a result of potentially facing a lose-lose outcome, many on Capitol Hill do not believe that the veto is a done deal. The White House has not issued an official position on the bill and spokespeople have been careful with their language, stopping short of issuing a full veto threat. “We have serious concerns with the bill as written,” a White House official said Wednesday.

“We believe there needs to be more careful consideration of the potential unintended consequences of its enactment before the House considers the legislation,” the official said. “We would welcome opportunities to further engage with the Congress on that discussion.”

The president has 10 days to either sign or reject the legislation before it becomes law.

Meanwhile, supporters of the legislation see it as a moral imperative.

“The victims of 9-11 and other terrorist attacks on US soil have suffered much pain and heartache, but they should not be denied justice,” Schumer said in a statement Wednesday. Under current U.S. law, victims may sue a country designated as a state sponsor of terrorism, like Iran. The bill would allow citizens to sue countries without that designation — like Saudi Arabia.

Fifteen of the 19 hijackers on 9/11 hailed from Saudi Arabia. Critics have long suspected that the kingdom’s government may have either directly or indirectly supported the attacks.

Congress in July released 28 previously secret pages detailing suspicious Saudi ties to the 9/11 hijackers, which made it very clear - according to a closer read of the document - that Saudi officials did indeed help plan and organize the attacks, even as the White House downplayed their involvement.

Saudi officials have for years denied that their government had any role in plotting the attacks and the Saudi government has led a quiet campaign in Washington to kill the legislation.

Despite its popularity in Congress, some prominent national security advisors have also pilloried the bill.

Former United Nations Ambassador John Bolton and ex-Attorney General Michael Mukasey, both of whom served under President George W. Bush, this week warned that the legislation “is far more likely to harm the United States than bring justice against any sponsor of terrorism.”

* * *

The real question, however, is not so much what Obama - who could potentially be branded a traitor if he proceeds with a veto as suggested, against the wishes of every single member of Congress, and the US population - will do, but how the Saudis, some of the most generous donors of the Clinton Foundation, will respond if the law indeed passes. As a reminder, in an epic media blunder, in early June, the Saudi Crown Prince admitted that Saudi Arabia had funded 20% of Hillary's presidential campaign, and will surely demand a quid pro quo in exchange. What Saudi vengeance may look like, should the generous Clinton donor's will not be obeyed, will be something Hillary's campaign will surely be very interested in.